While it's not possible to directly establish value overrides with some text, it can be achieved using Guides.
First of all you need to disable regular value axis value labels:
valueAxis.labelsEnabled = false;
Then you just need to add Guide objects for each value you need.
// GUIDE for 100 var guide = new AmCharts.Guide(); guide.value = 100; guide.lineColor = "#CC0000"; guide.label = "hello"; guide.inside = false; // this puts labels outside plot area guide.lineAlpha = 0; // this makes the actual guide line not to show valueAxis.addGuide(guide);
Here's a full working demo.